1. Field of the Invention
The present invention relates to an organic electroluminescence device capable of emitting light by converting electric energy to light, and also relates to a novel organic compound containing a silicon substituent.
2. Description of the Related Art
Since organic electroluminescence devices (hereinafter also referred to as “organic EL devices”) are capable of obtaining emission of light of high luminance by low voltage driving, they are actively researched and developed. An organic electroluminescence device comprises a pair of electrodes and an organic layer between the pair of electrodes, electrons injected from the cathode and holes injected from the anode are recombined in the organic layer, and generated energy of exciton is used for emission of light.
In recent years, increment in efficiency of devices has been advanced by the use of phosphorescent materials. As the phosphorescent materials, inventions in connection with phosphorescent devices using iridium complexes and platinum complexes are used as the phosphorescent material are described in U.S. Pat. No. 6,303,238 and WO 00/57,676. However, devices that satisfy compatibility of high efficiency and high durability are not yet developed.
As host materials capable of forming a light-emitting layer together with phosphorescent materials, invention relating to organic electroluminescence devices using materials having a triphenylsilyl group for imparting aptitude for vacuum deposition and an amorphous property are described in WO 05/022,962 and WO 04/095,598. However, these materials are low in the lowest excitation triplet energy (T1 energy) and when they are used with phosphorescent materials having emission of light in a blue region, they quench the emission of light of the phosphorescent materials to lower the luminous efficiency of the organic electroluminescence device. Therefore, these materials are inapplicable to a blue phosphorescent device, and further, they are low in charge injecting and transporting performances, so that the driving voltage of the device increases and the improvement is desired.
Invention concerning an organic electroluminescence device containing a compound represented by the following formula (F) is disclosed in JP-A-2006-135160 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.), and as the specific examples of the compounds, compounds represented by formula (F-31) or (F-33) in which an aromatic heterocyclic ring and a trimethylsilyl group are substituted on the ortho-position of the benzene ring are exemplified. However, durability of the devices using these compounds is not sufficient, and further improvement is desired.

In formula (F), each of Ar11, Ar12, Ar13, Ar14 and Ar15 independently represents an aryl group or an aromatic heterocyclic group; and R represents a group selected from a hydrogen atom, an aliphatic hydrocarbon group, a fluoroalkyl group, a halogen atom, a sulfonyl group, a silyl group, and a cyano group. However, when R represents a hydrogen atom or an aliphatic hydrocarbon group, at least one of Ar11, Ar12, Ar13, Ar14 and Ar15 represents an aryl group having one or more substituents having Hammett's σ para value of 0.05 or more.

Further, an organic electroluminescence device using Alq (an aluminum complex of 8-hydroxyquinoline) as an electron transporting material for use in an electron-transporting layer of a phosphorescent device is disclosed in Materials, Science and Engineering, C24 pp. 167-171 (2004). However, Alq is low in T1 energy and when Alq is used in a layer contiguous to a light-emitting layer, it quenches the emission of light of the phosphorescent materials to lower the luminous efficiency of the organic electroluminescence device. Therefore, materials high in T1 energy and applicable to the layer are also desired.